Melanoidins are polymeric and colored final products of the Maillard reaction, or “nonenzymatic browning reaction” consisting of a series of complex reactions that occurs during the heating of reducing sugars or carbohydrates together with amines, amino acids or proteins. Melanoidins are the compounds responsible for the brown color of roasted, baked, toasted, grilled, charred or browned foods, and are also common in many dietary liquids such as soy sauce, honey, wine, beer and coffee. Melanoidins are formed by cyclizations, dehydrations, retroaldolisations, rearrangements, isomerisations, and condensations that occur over the course of the Maillard reaction [Wang, H-Y, Qian, H, Yao, W-R. Food Chemistry, 2011, 128:573-584].
The structure of melanoidins is poorly defined, as these heterogeneous macromolecular compounds cannot be individually characterized. Three major proposals for their structure have been advanced: (i) polymers consisting of repeating units of furans and/or pyrroles, linked by polycondensation reactions; (ii) low-molecular-weight (LMW) colored substances cross-linked with proteins via s-amino groups, giving high molecular weight (HMW) colored melanoidins; and (iii) skeletons built up of sugar degradation products formed in the early stages of the Maillard reaction, polymerized through aldol-type condensation, and linked by amino compounds [Wang, H-Y, Qian, H, Yao, W-R. Food Chemistry, 2011, 128:573-584].
Being virtually ubiquitous in many food stuffs, there is interest in exploring the dietary function of melanoidins. They have been found to have a host of in vitro and in vivo functional properties, including: (i) free radical scavenging and antioxidant activity; (ii) anti-microbial activity; (iii) metal chelating ability; (iv) anti-microbial adhesion and anti-biofilm forming action; (v) lipid peroxidation inhibition; and (vi) inhibitory or promoting effects on activities of various enzymes.
Besides being ubiquitous in food stuffs, melanoidins have long been believed to be amongst the building blocks of humic substances, the brown colored macromolecular materials making up much of the natural organic matter in soil. Water soluble humic substances (humic and fulvic acids) are also an important part of the organic matter in aqueous environments and in atmospheric aerosol. Like humic and fulvic acids, melanoidins exert a partially anionic character in aqueous solution over a wide pH range. They can be separated into size fractions using dialysis, ultrafiltration or gel permeation techniques, with an arbitrary operational molecular weight cutoff of 10,000 or 12,400 Daltons for distinguishing between high molecular weight (HMW) and low molecular weight (LMW) melanoidins. Solubility of HMW melanoidins is enhanced at high pHs. At very low pH, the darker brown HMW melanoidins precipitate, while the LMW light straw colored melanoidins remain in solution. HMW melanoidins can also be flocculated by multivalent inorganic cations. Compared with humic substances, melanoidins are considerably more water soluble and have a much greater N content as a result of their derivation from amino acids.
Humic substances have been long reported to have positive effects on plant nutrition, seed germination, root initiation, and total plant biomass. For example, the ability of humic substances to chelate important plant micronutrients (Fe and Zn) and enhance their solubility in nutrient solution was found to enhance the growth of melons, soybean, and ryegrass. Humic acid was also found to have a transient effect on the transcriptional regulation of principal molecular agents involved in iron assimilation in non-Fe deficient cucumber plants. Humic acids, and particularly, low molecular weight humic acids, were found to increase the rate of nitrate uptake in wheat plants, apparently via the promotion of the molecular expression of proteins participating in nitrate support systems. In cucumber, humic acid application was associated with enhanced root H+-ATPase activity, increased nitrate shoot concentration, and decreased root nitrate concentration, effects accompanied by concomitant increases and decreases in several cytokinins and polyamines. Humic acids were reported to induce a partial relief from P starvation in tobacco BY-2 suspension cell cultures, increasing total cell phosphate amount, ATP and glucose-6-phosphate levels, and the activity of secreted acid phosphatases. Humic acid was also observed to impact root plasma membrane H+-ATPase activity and expression in maize, resulting in root growth promotion and proton pump activation, possibly due to the release of auxin-like plant growth promoters from the humic acids. Other evidence for auxin-like activity of humic substances is activation of the auxin synthetic reporter (DR5::GUS) and subsequent enhanced transcription of the early auxin responsive gene IAA19 in Arabidopsis, inducing lateral root formation.
No information is available regarding the effects of melanoidins on growth or functioning of plants.
Powdery mildew and Gray mold are two examples of fungal promoted diseases in plants. Said diseases are widespread and easily recognizable, causing serious damage to a wide range of plants, trees and agriculturally crops.
Powdery mildew is caused by plant pathogens (e.g., Oidium neolycopersici, an obligate parasite, i.e., the parasite attacks and can live only on living host tissues). Germination and infection are favored by fairly high humidity conditions. The fungus spreads very quickly in terms of a few days only. The conidia spread over short distances by wind and rain. The powdery mildew fungus grows on the surface of plant tissues. It penetrates the leaf surface with specialized cells called haustoria which gather nutrients and energy from the host leaf. Conidia are produced on the leaf surface within as little as 60 hours after initial infection and are carried by air currents to another leaf which they can directly infect by germinating.
Botrytis cinerea is another type of fungal pathogen which causes a widespread plant disease, damaging plants including agriculturally important crops, such as tomatoes and cucumbers. B. cinerea is the causal agent of gray-mold. Germination and infection of B. cinerea are favored by fairly high humidity and relatively cool conditions. Under these conditions, germination and infection can take place in a few hours.
Generally, when disease is severe, as it may be on tomato, cucumber or other crops, fungicidal sprays may be used to protect nearby healthy plants.
Typically, avoiding conditions of high humidity is the most effective way currently available to reduce the likelihood of spreading the diseases. However, there is no effective solution for controlling the diseases in affected plants once the disease is established.
Drought is one of the stresses that plants face while growing. Drought may be caused by limited availability of water or the inability of plants to absorb and transfer water to the canopy because of disturbed plant water relations and reduced water-use efficiency. It may also be caused by high temperatures or high vapor pressure deficit. Morphologically, plant reactions to drought conditions include reduced growth, for instance, as observed in plant height, leaf size and stem width. Under severe drought conditions, plants will wilt. In cases of severe wilt, leaves may not recover from the stress once plants are irrigated again, and the wilt thus results in death of leaves and other plant organs.
It has now been surprisingly found that melanoidins obtained from the Maillard reaction are active agents that can substantially improve plant properties.
It is therefore an object of the present invention to provide melanoidins and compositions comprising thereof that can be used for promoting plant well-being.
It is another object of the invention to provide melanoidins and compositions comprising thereof for use in controlling plant diseases.
It is still another object of the invention to provide melanoidins and compositions comprising thereof for use in protecting plants under drought conditions.
It is a further object of the invention to provide melanoidins and compositions comprising thereof for use in promoting plant growth.